The largest such study insofar has shown that prayer can actually harm you rather than help you. Researchers focused on the rates of recovery of heart bypass surgery patients and found that the patients who knew they were being prayed for had a slightly higher rate of complications.

Dr. Harold G. Koenig, director of the Center for Spirituality, Theology and Health at the Duke University Medical Center, criticized the study: "There are no scientific grounds to expect a result and there are no real theological grounds to expect a result either. There is no god in either the Christian, Jewish or Moslem scriptures that can be constrained to the point that they can be predicted.''

However, researchers themselves agreed to this idea and said that their study wasn't aimed at proving or disproving anything about God. They have only tested the effects of prayer on patients' health.

The study was financed by the Templeton Foundation which supports research into science and religion, and there were around 1 800 volunteers taking part in it, the largest such study. They were split into three groups: some who were prayed for and knew it, some who were prayed for but were told that this only might happen, and some who were not prayed for and were told also that there is only a possibility people would pray for them. Three Christian groups of volunteers have than prayed for specific patients for "a successful surgery with a quick, healthy recovery and no complications''.

Dr. Herbert Benson of Harvard Medical School and other scientists then looked for any complications within 30 days of the surgery. The ones who had no complications were equally divided among those who knew people prayed for them and those who knew it was only a possibility. In other words, prayer didn't help in any way the avoidance of complications. However, more people who knew they were prayed for developed complications - 59% of them developed complications versus only 52% in the case of those who were told it was just a possibility.

So, although this study didn't of course tested the supernatural side of prayer, it has showed that, from a medical point of view, knowing that somebody is praying for your recovery might actually harm you.